1. Field of the Invention
The present invention relates to a head adjustment method of adjusting a recording position of a line head (line bar) composed of a plurality of head modules, and a head-driving device and an image-forming device to which the method is applied.
2. Description of the Related Art
In a line head that is formed in an elongated strip shape by joining a plurality of head modules with each other, there is known a correction method of adjusting ejecting timing for each of head modules to correct displacement of a recording position caused by a variation (misregistration) of a mounting position of a head module in a direction parallel to a feeding direction of a paper sheet (referred to as a sub-scanning direction, or a Y-direction) (refer to PTLs 1 to 3).
In PTLs 1 (Japanese Patent Application Laid-Open No. 2006-116845) and 2 (Japanese Patent Application Laid-Open No. 2005-053167), with reference to a specific head module among a plurality of head modules, increase and decrease in ejecting timing of modules other than the specific module is controlled by adjusting a recording position in the Y-direction.
In PTL 3 (Japanese Patent Application Laid-Open No. 2006-305763), correction in the Y-direction is adjusted by controlling timing of each of the head modules with reference to a median line in the Y-direction in a print pattern. That is, according to the paragraph [0045] of PTL 3, an unit pattern recorded by each of the head modules is adjusted so that the center thereof is aligned with a main scanning direction (such as the center of a head unit) (refer to FIG. 9 of PTL 3).